Method for parameterizing a software damper for damping chatter vibrations

ABSTRACT

A method for parameterizing a software damper is disclosed. A target clutch torque affected in specified operating states by chatter vibrations is corrected by a software damper, wherein a transfer behavior of a clutch torque transferred via a friction clutch based on the target clutch torque is ascertained during a modulation of the target clutch torque. The software damper is parameterized with the help of the ascertained transfer behavior. To parameterize the software damper quickly and comprehensively, the target clutch torque is modulated by a broadband excitation in a frequency range of the chatter vibrations, and the transfer behavior is ascertained depending on operating parameters of the drivetrain.

BACKGROUND

The invention relates to a method for parameterizing a software damperconnected to a clutch control system for damping chatter vibrations of aclutch torque being transferred by means of an automated friction clutchwhich is controlled by the clutch control system by means of a targetclutch torque and which is positioned between a combustion engine and adrivetrain of a motor vehicle, wherein the target clutch torque affectedin specified operating states by chatter vibrations is corrected bymeans of the software damper, wherein a transfer behavior of a clutchtorque transferred via the friction clutch on the basis of the targetclutch torque is ascertained during a modulation of the target clutchtorque and the software damper is parameterized with the help of theascertained transfer behavior.

Automated friction clutches, for example friction clutches combined intoa dual clutch, are sufficiently well known and are inserted intodrivetrains having a combustion engine and a transmission, for examplean automated shift transmission, dual-clutch transmission or the like,between the combustion engine and the transmission. The friction clutchis operated in such cases by means of a clutch positioner as well as aclutch actuator. The clutch actuator is controlled by a clutch controlsystem. The clutch control system contains a regulator that operates thefriction clutch on the basis of a target clutch torque which can beobtained by means of a driving strategy program for example depending ona driver's desired torque, driving situations, road conditions and thelike, in such a way that a specified clutch torque is present at itsoutput.

Because of the properties of the friction clutch, the transmission andthe like, chatter processes may occur at the friction clutch whichresult in a vibration-accompanied transfer of the target clutch torquewith a fixed frequency response in a frequency range up to 30 Hz forexample.

In order to attenuate this frequency response, a method for reducingchatter vibrations is known from DE 10 2013 204 698 A1, in which anemulated vibration absorber, i.e., a software-based vibration absorber,is superimposed on the clutch positioner for the target clutch torque asa software damper.

Knowledge of the drivetrain behavior and of the transfer behavior on thebasis of the target clutch torque is necessary for system identificationand design. In order to ascertain this transfer behavior, chattervibrations are simulated by modulating the target clutch torque anddrawing upon the resulting signals which are relevant for drivingcomfort, for example the longitudinal acceleration of the motor vehicleor the transmission input speed, to design and parameterize the softwaredamper, for example a regulator or filter.

This purpose is served by modulations of the target clutch torque in therelevant frequency range of chatter vibrations, typically between 2 Hzand 30 Hz. Here, a frequency response of the system is determined, forexample over a control link beginning with the clutch control system,through the clutch positioner, through the friction clutch subject tochatter vibrations to its output, for example a transmission input shaftvibrationally coupled, by carrying out for time periods of typically afew seconds a sinusoidal excitation having a fixed frequency in thedesired operating state on the clutch torque for example with a stepwidth of 0.5 Hz across the relevant frequency range of the chattervibrations in relevant operating states, for example moving off andcreeping situations and when engaging the clutch after gear changes. Theevaluation of the transfer behavior is carried out largely by hand, byrelating the amplitudes of modulation torque and transmission inputspeed or longitudinal acceleration to each other in acomponent-by-component examination of the frequency components accordingto a discrete Fourier transformation. This yields a transfer functionwhich is used for parameterizing the software damper. This method isvery time-intensive.

SUMMARY

The object of the invention is to advantageously refine a method fordesigning and parameterizing a software damper.

The object is fulfilled by the features of the invention. Advantageousembodiments of the method are described below.

The proposed method serves to parameterize a software damper connectedto a clutch control system, which is intended for damping chattervibrations of a clutch torque. The clutch torque is transferred througha friction clutch positioned between a combustion engine and atransmission in a drivetrain of a motor vehicle, depending on a targetclutch torque specified from a driving strategy. The friction clutch iscontrolled by a clutch positioner by means of a position controller,whose input signal is, among other things, the target clutch torque andwhose output signal is an actuation travel or the like. Superimposed onthe position controller is the software damper, which corrects chattervibrations that occur in specified operating states by correcting theloaded target clutch torque. To parameterize the software controller, atransfer behavior of the clutch torque across the system, in particularthe friction clutch, is obtained, in which the target clutch torque ismodulated by means of vibrations in the range of chatter vibrationfrequencies that are expected, modeled or obtained empirically on themotor vehicle. On the basis of the ascertained transfer behavior, thesoftware damper is then identified and parameterized. In order toachieve a quick and comprehensive parameterization, the target clutchtorque is modulated by means of a broadband excitation in a frequencyrange of the chatter vibrations, and the transfer behavior isascertained depending on operating parameters of the drivetrain.

The proposed method for exciting the control link, for example thedrivetrain, provides for the use of a broadband signal instead of thepreviously used fixed-frequency sine functions to modulate the targetclutch torque, which is modulated in the relevant operating state of thechatter vibrations to the clutch torque which results from the drivingstrategy.

The spectrum relevant for the system identification is covered over theentire determination of the transfer behavior by this continuousbroadband excitation. In this way, a greatly improved frequencyresolution in the transfer function is achieved in a significantlyshortened testing time. At the same time, in a preferred manner, amaximum amplitude of the target clutch torque is held to a specifiedfixed value.

Various advantageous methods may be provided for implementing abroadband excitation of the system of this sort. In a first form of theexcitation, a pseudorandom binary sequence (PRBS) can be modulated up tothe target clutch torque. PRBS is understood to mean a binary signalwhich shares the spectrum of white noise. The PRBS consists essentiallyof two signal levels, between which the system switches, for example, ina 20 ms rhythm. This switching between the levels results in arectangular modulation, which is distinguished in the spectrum by anamplitude dependency of the form

$\frac{\sin\;\left( {\frac{\pi}{50\mspace{14mu}{Hz}} \cdot v} \right)}{v}$with the frequency v. However, because of the rapid switchover time of20 ms this dependency becomes noticeable only at frequencies startingaround 50 Hz, since the first frequency components disappear here. Thespectrum of the PRBS signal described here is present at any time. As aresult, the required duration of the experiment is determined only bythe frequency resolution desired in the transfer function. This applies,according to the interconnections of the discrete Fouriertransformation, for the entire duration T_(Ex)=1/Δv of the determinationof the transfer behavior, where Δv is the desired frequency resolution.Additional measuring time increases the signal-to-noise ratio.

A preferred embodiment of a broadband excitation may be designed in theform of a sinusoidal signal with time-relevant frequency, for example inthe form of a so-called sine sweep. In this case, the frequency ischanged continuously in the frequency band desired for the transferbehavior. This continuous modification makes it possible to cover thecomplete frequency band within a relatively short period of time.

In addition, preferred embodiments of a broadband excitation may beprovided, for example, by means of adaptive filtering, for example bymeans of transverse filtering using an LMS algorithm (least mean squaresalgorithm). Excitation sources for determining the transfer behavior maybe in particular pulse responses of the clutch torque or of the targetclutch torque to stored pulses obtained during driving operation of amotor vehicle.

The transfer behavior of the drivetrain is of central importance forsuccessful anti-chatter control. By ascertaining the transfer functionor transfer behavior with sufficient precision, the software damper, forexample in the form of a regulator or filter, can be parameterized withsuch stability and robustness that additional excitations are unlikely.

To achieve an adaptation of the software damper to a transfer behaviorof the drivetrain which changes depending on operating states of themotor vehicle, depending on the existing target clutch torque, to thetransmission input speed or the vehicle acceleration, it is proposed ifpossible that all operating states that change the transfer behavior beincorporated into this determination.

For the most comprehensive possible determination of the transferbehavior and the associated parameterization of the software damper, thetransfer behavior can therefore be determined depending on operatingstates and parameters of the control link, of the drivetrain, andultimately of the entire motor vehicle and its components which arejoined in a vibratory interconnection. In a preferred form, the transferbehavior can be ascertained, in a non-final enumeration, depending on amean torque transmitted via the friction clutch, a selected gear of thetransmission, masses of the drivetrain that are coupled with each other,for example auxiliary units of the combustion engine that can beconnected and disconnected, a hybrid module and the like, on masses thatare coupled vibrationally with the drivetrain, for example the vehiclebody with a vehicle mass, a trailer of the motor vehicle and the like,on at least one temperature of a component of the drivetrain, forexample the temperature of the clutch positioner, the friction clutch,the combustion engine and/or the transmission or the like, on a drivingresistance of the motor vehicle, for example the tire properties, thetire pressure or the like.

The target clutch torque specified by the driving strategy acts here asa pre-load, which corresponds to a pre-stressing of the drivetrain. Thisovercomes any free play and places elastic elements in the drivetrainunder stress—this influences the transfer behavior of the drivetrainsignificantly. As a result, the transfer behavior is determineddepending on the transferred clutch torque, for example at differentpre-loads—i.e., at different operating points of the friction clutch.

Since the drivetrain has a transmission ratio that depends on the gear,the coupling of the masses contained in the drivetrain differs withdifferent choices of gears and their transmission ratios. Furthermore,in the case of a dual-clutch transmission, the aggregate of the coupledvibratory masses changes when a gear is engaged or disengaged on theinactive shaft. This likewise influences the transmission behavior ofthe drivetrain, in that activating a gear lowers the resonant frequency,while disengaging an additional gear raises the frequency, so that thetransfer behavior is determined depending on this.

Since the vehicle in its entirety is part of a vibratory system, itsmass influences the transfer behavior. This must be taken into accountin the event of a corresponding change in the total mass. Recognition ofa change of the vehicle mass may be part of an integrated regulatorconcept, for example in that the vehicle mass is taken into account inthe transfer behavior by means of a drivetrain observer from a clutchtorque model. The recognition can take place through evaluation of acombination of signals and an observer structure. Relevant measurementsignals include, for example, engine torque, engine speed, transmissionspeed, acceleration of the motor vehicle and also additional informationsources, for example seat occupancy detection and/or the like.

The slope which the motor vehicle has to overcome during the process ofmoving off plays an important role with regard to the transfer behavior,since, for example, the combustion engine braces against its bearings ina different manner than is the case on the flat. This changes thevibration modes of the engine mass, and the transfer behavior of thedrivetrain changes. Like the changed vehicle mass, this can be detectedon the basis of the acceleration of the motor vehicle, for example bymeans of an acceleration sensor, and may be included in determining thetransfer behavior.

Since the entire system of the motor vehicle is affected by chattervibrations, the tires mounted on the motor vehicle also influence thesevibrations and thus also the transfer behavior. At the same time, thechanged rolling resistance plays a central role. The rolling resistance,for example, and/or similar parameters, are therefore taken into accountwhen determining the transfer behavior. The tire pressure is often knownin modern vehicles through corresponding sensors in the tires, and cantherefore be available for the transfer function.

Besides the change due to the vibratory total mass—the influence hereshould be analogous to that of the changed vehicle mass—the use of atrailer makes an additional source for changes to the vibratory system.This results from the fact that when the body of the vehicle vibrates,the trailed mass may also vibrate for example contrary to the vehicle,and may thereby fundamentally change the resonance behavior, so thatoperation with a trailer is advantageously accounted for accordinglywhen determining the transfer behavior.

If a possibly available four-wheel drive is engaged, the masses coupledin the system change and thus also the vibration and transfer behavior.Furthermore, it can be assumed that the rigidities contained in thesystem are intensified. This can be taken into account in the case inquestion in determining the transfer behavior.

In the case of an activatable hybrid module, the sum of the coupledmasses changes when it is activated. In addition, the electric motor mayprovide for additional damping in the system, or may even influence thesystem behavior actively through its actuation. These factors influencethe transfer function of the drivetrain, and are taken into account inthe link identification and the parameterization.

The temperatures in the positioning and transfer elements influence thevibration behavior, because friction/damping change accordingly. Forexample, known temperatures of the actuator, the friction clutch, theenvironment and/or the like may be registered and included indetermining the transfer behavior.

Through activatable units which may possibly be used in the motorvehicle, such as an air conditioner, recovery module and the like,additional masses may be coupled to the drivetrain, and under certaincircumstances additional damping elements may be linked in. In thiscase, this results in changed dynamics of the drivetrain which is takeninto account beneficially with regard to determining the transferbehavior.

Going beyond system identification and determining the transferbehavior, during operation the activation and deactivation of theanti-chatter control system may be controlled meaningfully. To this end,controllable and non-controllable driving situations are identified anddetermined. The definition of a non-controllable driving situationoccurs when designing the software damper in conjunction with a systemidentification. These driving situations can be recognized whiledriving, so that a corresponding deactivation of the software damper canbe carried out. At the same time, possible occurrence of a deteriorationof driving comfort—for example through abrupt on-and-off switching ofthe software damper—will be prevented, for example, by a continuoustransition between on and off states of the regulator, which is achievedthrough a continuous increasing and reducing of the totalintensification factor. This transition is initiated upon reaching anon-controllable state, and likewise upon reaching a controllable stateagain.

Furthermore, unwanted effects that can result in a possible recouplingwith the resonant frequency of the system may be attenuated, so thatthey are not recognized by the software damper. This comes about, on theone hand, through firm shut-off conditions and, on the other hand,through suitable time filtering of the input signals of the softwaredamper. The shut-off conditions relate here to a minimum rotationalspeed below which the control system is deactivated, since in thisrange, due to technical reasons of the speed measurement, the signalquality decreases severely and reliable regulation can no longer beguaranteed. In addition, a certain minimum slip speed is preferably setat the friction contact of the friction clutch, so that sticking of thefriction clutch and thus unwanted additional excitations of the naturalfrequency of the drive train are avoided. Since, if chattering occurs,the proposed shutoff conditions are exceeded and again under-run by thechatter frequency, the regulator would accordingly be switched on andoff with the chatter frequency. This would introduce an additionalexcitation of this frequency, and that would further destabilize thesystem. The shut-off process therefore takes place instantaneously,while switching the regulator on again is temporally debounced. In doingso, the shut-off condition must be violated continuously again for acertain period of time, so that the overall intensification factor iselevated again. This prevents a continuous switching on and off of theregulator.

Furthermore, the regulator may be shut off or attenuated for reasons ofstability, if the clutch characteristic on which the driving state isbased has too high a slope. This too-steep course could make theresolution of the clutch actuation too coarse for an appropriatemodulation torque, which would make an overdriving of the softwaredamper possible, and thus a negative influence on the stability of thesystem. Therefore no regulation takes place in this case.

Analogously or in addition thereto, in addition the entire modulationtorque introduced by the software damper may be limited by an internalcharacteristic, so that possible identified excessive and thus no longercontrollable modulation torques cannot be introduced into the targetclutch torque to their full extent.

Another stability-relevant action may be reinstallation of the softwaredamper. In order to avoid any errors in the phase position of the activeregulating signal with regard to the chatter vibration to be regulated,the regulator is reinstalled when the active friction clutch of adual-clutch transmission is replaced. This makes it possible to detectand compensate appropriately for changes in the chatter characteristicswhich are to be expected due to the clutch replacement, independent ofthe previous behavior.

Furthermore, for stable regulation of the software damper, the runningtime of the regulating algorithm as part of the vehicle software in thecontrol device of the vehicle may be minimized. The faster theanti-chatter component runs in the control device, the faster it canrespond to changes in the system and its behavior. Furthermore, it mustbe guaranteed that the memory requirement of the regulator component iskept as small as possible. This, and the two different timings oftenused in the control device, result in the necessity of conceiving thesoftware damper in such a way that time-critical parts of the regulatingalgorithm are executed at the faster of the two available speeds, sothat the fastest possible response to changes in the input values isguaranteed. The less time-critical parts of the software damper, on theother hand, are executed at the slower speed, in order to save bothmemory and processor resources and to optimize the total running time ofthe regulator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in further detail on the basis of theexemplary embodiment depicted in FIGS. 1 through 4. The figures show thefollowing:

FIG. 1 a time sequence of a sine sweep,

FIG. 2 a diagram to depict a broadband excitation of the target clutchtorque by means of a linear feedback shift register to generate a PRBSsignal,

FIG. 3 a diagram with the time sequence of a PRBS signal that modulatesthe clutch torque,

and

FIG. 4 a diagram with the spectrum of a PRBS signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The sine sweep shown in FIG. 1 is created by means of a signalgenerator. A sinusoidal signal with a specified frequency and torqueamplitude is produced. In the exemplary embodiment shown, the frequencyis increased in a fixed interval, which results in a stepped frequencypattern. The frequency range used typically lies between 1.5 Hz and 30Hz, which yields the modulated signal shown. This procedure yields avery broadband spectrum, which makes it possible to obtain the mostdetailed possible frequency response of the system over the controllink.

FIGS. 2 through 4 show an alternative method to the method in FIG. 1, inorder to achieve a broadband excitation of the target clutch torque.This method is based on the excitation using a pseudorandom binarysequence (PRBS) signal. To this end, a so-called linear feedback shiftregister (LFSR) is implemented, which outputs zero or one quasi atrandom after every call. This generates a randomly varying signal levelwith a given amplitude. The linear feedback shift register shown in FIG.2 is realized by a binary-interpreted number of desired magnitude. Thefollowing values are generated by first capturing certain places in thenumber dependent on the length of the register, and joining them into anew bit by means of appropriate logical links. This new bit is theninserted at the beginning of the register, and the rest of the bits areeach displaced by one position. A random level is realized by thecapture of the last bit. In FIG. 3, the random level S is added to thetarget clutch torque from a driving strategy to set a static clutchtorque at the friction clutch. By means of this modulation, anexcitation of the drivetrain is achieved with a broadband modulation ofthe clutch torque. The level S depicted in FIG. 3 represents arectangular modulation, which is distinguished in the spectrum by anamplitude dependency of the form

$\frac{\sin\;\left( {\frac{\pi}{50\mspace{14mu}{Hz}} \cdot v} \right)}{v}.$

The switchover time of 20 ms causes the amplitude dependency to becomenoticeable only at frequencies starting around 50 Hz, since the firstfrequency components disappear here.

FIG. 4 shows the spectrum of the PRBS signal for this. This is presentat any time. As a result, the required duration of an experiment toascertain the transfer behavior of the modulated target clutch torque isdetermined essentially by the frequency resolution desired in thetransfer function and the desired signal-to-noise ratio. This applies,according to the interconnections of the discrete Fouriertransformation, for the minimum entire duration T_(Ex)=1/Δv of theexperiment, where Δv is the desired frequency resolution. For a typicalmeasurement of adequate quality for designing and parameterizing thesoftware damper, a measurement period of typically at least 30 s isused.

The invention claimed is:
 1. A method for parameterizing a softwaredamper connected to a clutch control system for damping chattervibrations of a clutch torque being transferred by an automated frictionclutch which is controlled by the clutch control system by a targetclutch torque and which is positioned between a combustion engine and adrivetrain of a motor vehicle, comprising correcting the target clutchtorque affected in specified operating states by chatter vibrations bythe software damper, including ascertaining a transfer behavior of theclutch torque transferred via the friction clutch on the basis of thetarget clutch torque during a modulation of the target clutch torque,parameterizing the software damper with the ascertained transferbehavior, modulating the target clutch torque by a broadband excitationin a frequency range of the chatter vibrations, and ascertaining thetransfer behavior depending on operating parameters of the drivetrain.2. The method according to claim 1, further comprising generating thebroadband excitation by a PRBS signal.
 3. The method according to claim1, further comprising generating the broadband excitation by asinusoidal signal with time-variable frequency.
 4. The method accordingto claim 1, further comprising ascertaining the transfer behaviordepending on a mean clutch torque.
 5. The method according to claim 1,further comprising ascertaining the transfer behavior depending on aselected gear of the transmission.
 6. The method according to claim 1,further comprising ascertaining the transfer behavior depending onmasses of the drivetrain which are coupled with each other.
 7. Themethod according to claim 1, further comprising ascertaining thetransfer behavior depending on masses of the drivetrain which arecoupled vibrationally with the drivetrain.
 8. The method according toclaim 1, further comprising ascertaining the transfer behavior dependingon at least one temperature of a component of the drivetrain.
 9. Themethod according to claim 1, further comprising ascertaining thetransfer behavior depending on a driving resistance of the motorvehicle.